The present invention relates to a prosthetic device adapted for use on a lower extremity amputee. More particularly, the present invention is directed to an artificial ankle, and on a prosthetic leg device incorporating the ankle, that pivots to provide an amputee with an improved gait for running or walking. The present invention also enables a leg amputee to more easily ascend and descend staircases.
Throughout modern human history, appropriate medical care sometimes has required amputation of a diseased or damaged limb. When a leg or portion thereof was amputated, often, the leg amputee was fitted with a prosthetic leg device so that the amputee could walk without the use of crutches or other aid devices. An early prosthetic leg device was simply a peg affixed to the remaining portion of the amputated leg of the amputee. Although effective, a xe2x80x9cpeggedxe2x80x9d leg was not aesthetically pleasing.
Technological advancements of new materials enabled other types of prosthetic leg devices to be developed which were more aesthetically pleasing. Typically, these prosthetic leg devices included a calve portion, an ankle and a foot structure that simulated a human leg. Skillful fabrication of these prosthetic leg devices with advanced materials made them appear to be a real leg with a real foot structure. The advanced material which formed the anatomically-correct parts of the human body was either a plastic material or a rubber-like material having a color texture of human flesh. Now, a sock and footwear could be worn on the artificial foot to match the ones on the healthy foot so that the general public would be unable to visually determine that a person was an amputee.
Even though these new prosthetic devices appear generally life-like, several disadvantages remain. First, in order to assure proper balance,the lower leg portion below the xe2x80x9ckneexe2x80x9d is rearwardly offset from the upper leg portion above the xe2x80x9ckneexe2x80x9d. Therefore, when simply standing, the artificial foot is positioned to the side of and behind the real foot, that is, in a staggered orientation, which presents an unnatural appearance. More importantly, though, none of these devices could perform functionally as well as a human leg. Unlike the function of a healthy human ankle, the typical ankle of the prosthetic leg device is a rigid, 90-degree connection unable to provide any pivotal movement between the calve portion of the leg and the foot structure. To use prior art prosthetic leg devices, the amputee is required to angularly swing his/her amputated leg in an arcuate motion relative to his/her healthy leg when making a step with the prosthesis. This arcuate motion, although unnatural, is necessary so that the prosthesis can be lifted above the walking surface to avoid being dragged when stepping. This arcuate motion adds stress to the healthy knee, leg and ankle of the amputee that could result in chronic pain and further injury. Thus, a tradeoff occurs. For a more aesthetically-pleasing prosthetic leg device, the amputee must suffer pain and/or risk future damage to his/her healthy leg.
A normal gait cycle of a human being includes three general phases which are dorsiflexion, plantarflexion and xe2x80x9cpush-offxe2x80x9d. Each of these phases is explained relative to an angular position, of the foot relative to a shin bone pivotally connected thereto by an ankle joint. The foot, of course, includes a heel disposed proximate to the ankle joint and a sole disposed distally to the ankle joint. The human foot is considered to be in a neutral position when it forms a 90-degree angle with the shin bone relative to a pivotal axis of the ankle joint. Dorsiflexion occurs when an acute angle is formed between the foot and the shin bone relative to the pivotal axis of the ankle joint. For example, dorsiflexion is best demonstrated during stepping as the heel on the foot of the advancing leg first contacts the walking surface immediately before the body weight of the amputee is transferred to the foot. Plantarflexion occurs when an obtuse angle is formed between the foot and the shin bone relative to the pivotal axis of the ankle joint. Plantarflexion is best demonstrated when the ankle of the advancing leg bends immediately after the heel contacts the walking surface so that both the heel and sole of the foot contact the walking surface in preparation of receiving the body weight of walking person. xe2x80x9cPush-offxe2x80x9d occurs as the trailing leg completes its step whereby the ankle joint becomes xe2x80x9clockedxe2x80x9d with the foot and shin bone in the neutral position so that the sole of the foot can propel the body weight of the walking person forward to transfer it onto the advanced leg.
Since prior art leg prosthetic devices are permanently fixed in the neutral position, effective xe2x80x9cpush offxe2x80x9d occurs so that the amputee can complete his step and repeat his/her gait cycle. Unfortunately, none of the prior art prosthetic leg devices known to the present inventor provides dorsiflexion or plantarflexion. This lack of dorsiflexion and plantarflexion requires the amputee to swing the prosthetic leg outwardly in the arcuate fashion as described above when stepping. Furthermore, the lack of dorsiflexion and plantarflexion further hinders the amputee when ascending or descending stairs. With prior art prosthetic leg devices, an amputee is well advised to descend stairs one at a time by first lowering the prosthetic leg onto the next lower step before advancing the trailing healthy leg thereonto. Correspondingly, the amputee should ascend stairs one at a time by first raising the healthy leg on the step disposed immediately above before advancing the prosthetic leg thereon. It is extremely perilous for an amputee with a prosthetic leg to attempt to ascend or descend stairs by stepping on alternate steps with each leg. For example, descending stairs by an amputee with a prosthetic leg device in an alternating matter tends to thrust the amputee""s body weight forward which could result in falling down the stairs. This thrusting effect is due to the absence of dorsiflexion.
Prior art prosthetic leg devices inhibit amputees from. participating in various sporting events which require running. Not only is it difficult, if not impossible, to run in a prior art prosthetic leg device but also the rigidity of construction provides limited shock absorption capabilities. Much of the induced shock is absorbed by the body of the amputee that, in turns, causes further stress on the amputee""s body. Such rigidity also results in minimal flexibility of the prosthetic leg device. Again, the amputee""s body must compensate for this lack of flexibility.
There is a need in the marketplace to provide an artificial ankle joint that can be used with a prosthetic leg device so that a foot structure thereof can pivot about pivotal axis relative to a prosthetic leg portion. There is a further need in the marketplace to provide an artificial ankle joint for a prosthetic leg device which can execute the three general phases of dorsiflexion, plantarflexion and xe2x80x9cpush-offxe2x80x9d to simulate a gait cycle of a normally healthy human being. It would be advantageous if this prosthetic leg device could be used for walking and running as well as ascending and descending stairs. It would be further advantageous if this prosthetic leg device could absorb shock and be flexible so as to relieve the amputee""s body from absorbing shock and compensating for any lack of flexibility. There is a need to provide with such an ankle joint, and to provide a prosthetic leg device with such an ankle joint which prosthesis is lightweight. The present invention satisfies these needs and provides these advantages.
It is an object of the present invention to provide a new and useful artificial ankle joint for use with a prosthetic leg device having a foot structure and a proximal end portion so that the foot structure can pivot about a pivotal axis relative to the proximal end portion of the prosthetic leg device.
Another object of the present invention is to provide an artificial ankle for use with a prosthetic leg device which can execute the dorsiflexion, plantarflexion and xe2x80x9cpush-offxe2x80x9d phases of a human gait cycle.
It is a further object of the present invention to provide an artificial ankle joint that can lock at a locking position so that the xe2x80x9cpush-offxe2x80x9d phase of the human gait cycle can be executed.
It is yet another object of the present invention to provide an artificial ankle joint which automatically unlocks when the xe2x80x9cpush-offxe2x80x9d phase of the gait cycle is completed.
A still further object of the present invention is to provide an artificial ankle joint which employs the body weight of the amputee to lock the artificial ankle joint at the locking position when executing the xe2x80x9cpush-offxe2x80x9d phase of the gait cycle.
Yet another object of the present invention is to provide an artificial ankle joint which locks in the locking position only when a certain threshold of load is present.
Yet a still further object of the present invention is to provide an artificial ankle joint which can be disengaged from locking at the locking position regardless of the amount of load induced thereon.
Yet another object of the present invention is to provide an artificial ankle joint with a prosthetic leg device which can allow an amputee not only to walk and run similarly to a healthy human being but also ascend and descend stair cases like a healthy human being.
Still further, another object of the present invention is to provide an artificial ankle joint operative with a prosthetic leg device which is lightweight and aesthetically pleasing.
Another object of the present invention is to provide an artificial ankle joint that can absorb shock and can slightly flex in three dimensions.
According to the present invention, an artificial ankle joint and a prosthetic leg device incorporating such an artificial ankle joint is described for use on a human amputee. The prosthetic leg device has a proximal end portion and a foot structure, and the ankle joint is located between the proximal end portion and the foot structure. Broadly, the ankle joint includes a matable socket and head assembly interconnecting the proximal end portion and the foot structure for relative pivotal movement about a pivot axis between first and second pivot positions. The socket and head assembly includes a socket disposed on either the proximal end portion or the foot structure and a head disposed on the other. Preferably, the socket is disposed on the foot structure and the head is disposed on a distal end of a shaft that is secured to the proximal end portion. In any event, the head is sized to be matably received by the socket.
In order to assist the amputee during walking, a load sensitive locking mechanism is associated with the socket and head assembly. This locking mechanism is operative in response to a triggering compressive force between the socket and head in excess of a threshold magnitude to cause the socket and head assembly to lock at a selected locking position between the first and second pivot positions. When so locked, the locking mechanism prevents relative pivotal movement of the socket and head, but, in the absence of the triggering compressive force, the locking mechanism freely permits relative pivotal movement of the socket and head between the first and second positions.
Further, to assist the amputee in walking, the present invention provides a spring element associated with the socket and head assembly. This spring element resiliently biases this socket and head into the first pivot position. This first position corresponds to a dorsiflexion or xe2x80x9ctoes-upxe2x80x9d position wherein the foot structure is oriented at an acute angle relative to the shin of the artificial prosthetic. The second rotational position of the socket and head assembly thus corresponds to a plantarflexion state wherein the foot structure is at an obtuse position. When in the locked position, the foot is at the neutral position generally at a 90-degree angle with respect to the shin of the artificial leg prosthetic. To further assist the amputee, it is preferred that the socket itself be received in a socket housing with a layer of stiff, yet resilient first material being interposed between the socket and the socket housing to imitate cartilage in the natural ankle joint. Moreover, the foot structure itself may be constructed of a stiff, yet resilient material to slightly flex during the walking motion, again to imitate the natural foot.
In its more detailed construction, the artificial prosthetic leg device of the present invention includes a prosthetic socket having a socket sized and adapted to releasably receive and retain the remaining residual limb portion of the amputated leg of the amputee. A shaft then extends along a central axis of the artificial leg, and the general region of the shin, and terminates in a head portion that forms one-half of the artificial ankle joint. The socket housing, the socket element and the first resilient material is then mounted on the foot structure opposite the toe portion thereof to define the other half of the artificial ankle joint. The socket includes an arcuate sidewall against which an outer peripheral surface of the head pivots. Here, the locking mechanism is preferably formed by a recess in the arcuate sidewall and a latch assembly carried by the head and shaft. When the triggering compressive force is present, the latch assembly then engages the recess at the selected locking position. The latch assembly preferably has a first rod slidably disposed in a bore formed axially through the shaft and has a latch element connected to a first end of the first rod. The latch element may be a rod-shaped member extending perpendicularly to the central axis. The first rod is resiliently biased to retain the latch element in a retracted state within a channel formed in the outer peripheral surface of the head parallel to the pivot axis so that, in the locked position, the latch element can move from the retracted state to an extended state thereby to engage the recess in the socket sidewall. The latch assembly may also include a second rod slidably disposed within the bore and extending outwardly therefrom opposite to the first rod. A first coil spring is operative to bias the first rod into the retracted state and a second coil spring is operative to resiliently retain, the first and second rods in spaced-apart relation from one another. The first coil spring has a spring constant that is preferably equal to-or greater than the spring constant of the second coil spring.
A restraining assembly may also be provided and associated with the locking mechanism. The restraining assembly operates in a restrained state to disable the locking mechanism so that the head and socket are permitted to pivot freely between the first and second positions while bypassing the locking position. In an unrestrained state, the locking mechanism is enabled. The restraining assembly in the exemplary embodiment includes an annular first collar connected to and extending around the shaft in stationary condition. An annular second collar is connected to the locking mechanism and is slidably received and rotatably mounted on the shaft. Each of the first and second collars have a plurality of alternating and longitudinally extending teeth and gaps therebetween. The teeth and gaps are sized so that respective ones of the teeth on each of the first and second collars will facially contact each other when the second collar is rotated into a first angular position to orient the restraining assembly in the restraining state. By virtue of the contact between the teeth, load forces are transferred away from the locking mechanism so that it is not subjected to the triggering compressive force. However, when the second collar is rotated to a second angular position to orient the restraining assembly in the unrestrained state, respective ones of the teeth on each of the first and second collars may slidably move into and out of respective ones of the gaps thereon thereby enabling the locking mechanism to receive the load and therefore the triggering compressive force. The restraining assembly may include a bushing slidably received in the shaft, a cap slidably received on the shaft and a retainer ring slidably disposed over the cap and releasably connected to the second collar so that the retainer ring and the second collar are rotatably connected to the cap and can rotate about the bushing and the shaft. The bushing can have a bushing channel formed in an outer peripheral bushing edge thereof. The second collar may include a set screw operably connected to the second collar through an outer peripheral collar edge. The set screw and bushing channel are operative to releasably retain the restraining assembly in the selected one of the retained and unretained states.
These and other objects of the present invention will become more readily appreciated and understood from a consideration of the following detailed description of the exemplary embodiments of the present invention when taken together with the accompanying drawings, in which: